The reduced coenzyme Q10 (I) and the oxidized coenzyme Q10 (II) are mitochondrial electron transport system-constituting factors in cells of a living body of human and deal with ATP production by working as electron carriers in oxidative phosphorization reactions.
Conventionally, oxidized coenzyme Q10 has been widely used for supplementary nutrient foods and cosmetic products in addition to pharmaceutical products as a pharmaceutically and physiologically effective substance for a variety of diseases.
On the other hand, reduced coenzyme Q10 has not so much drawn attention so far; however, in these years, there has been reported that reduced coenzyme Q10 is more effective in various applications than oxidized coenzyme Q10.
For example, Japanese Kokai Publication Hei-10-330251 discloses an antihypercholesterolemia agent having excellent cholesterol reducing function, an antihyperlipemia agent, and an agent for curing and preventing arteriosclerosis which contain reduced coenzyme Q10 as an active ingredient. In addition, Japanese Kokai Publication Hei-10-109933 discloses a pharmaceutical composition excellent in oral absorbability comprising coenzyme Q10 including reduced coenzyme Q10 as an active ingredient.
Furthermore, reduced coenzyme Q10 is effective as an antioxidant and a radical scavenger. R. Stocker, et al. have reported that reduced coenzyme Q10 prevented peroxidation of human LDL more efficiently than α-tocopherol, lycopene and β-carotene (Proceedings of the National Academy of Science of the United States of America, vol. 88, pp. 1646-1650, 1991).
It has been known that oxidized coenzyme Q10 and reduced coenzyme Q10 are in a certain type of equilibrium in a living body and that oxidized coenzyme Q10/reduced coenzyme Q10 absorbed in the living body are mutually reduced/oxidized.
Reduced coenzyme Q10 is supposedly produced by a chemical synthesis method, similarly to the process for producing oxidized coenzyme Q10. But the synthesis process is supposed to be complicated, risky and costly. Moreover, in the case of chemical synthesis methods, it will be necessary to minimize the subgeneration and contamination of a (Z)-isomer, which is suspiciously unsafe (Biomedical and Clinical Aspects of Coenzyme Q, vol. 3, pp. 19-30, 1981). Europe Pharmacopoeia regulates that a content of (Z)-isomer in oxidized coenzyme Q10 must be not more than 0.1%.
As another process for producing reduced coenzyme Q10, it can be supposed a method of utilizing microbial cells, that is, a method for separating and recovering reduced coenzyme Q10 from reduced coenzyme Q10-producing microorganisms. However, the reduced coenzyme Q10 produced by the microbial cells of the above-mentioned microorganisms contains a large amount of oxidized coenzyme Q10, and the separation and recovery of reduced coenzyme Q10 by a conventional method results in high cost.
The following are documents describing the presence of reduced coenzyme Q10 in microbial cells and there have been known the following examples of bacteria.    (1) An example describing that at lowest 5 to 10% by weight and at highest 30 to 60% by weight of reduced coenzyme Q10 are present among the entire coenzymes Q10 in culture cells of photosynthesis bacteria (Japanese Kokai Publication Sho-57-70834).    (2) An example describing that the genus Pseudomonas is subjected to thermal extraction by an organic solvent in the presence of sodium hydroxide and pyrogallol, and the resultant is treated with 5% sodium hydrosulfite solution, and further dehydrated and concentrated to collect an acetone-soluble portion, and an oil containing reduced coenzyme Q10 is obtained (Japanese Kokai Publication Sho-60-75294).
Both of the above (1) and (2) aim to convert a mixture of the obtained reduced coenzyme Q10 and oxidized coenzyme Q10 or the obtained reduced coenzyme Q10 into oxidized coenzyme Q10 by further oxidation. Thus, reduced coenzyme Q10 is only described as an intermediate substance in producing oxidized coenzyme Q10.
In the above (1), photosynthesis bacteria are used, the culture of which is complicated. Furthermore, in the microbial cells of the above-mentioned microorganisms, when the production of reduced coenzyme Q10 is aimed at, it cannot be said that the ratio of reduced coenzyme Q10 among the entire coenzymes Q10 is sufficient.
The above (2) comprises a process of converting oxidized coenzyme Q10 contained in a hexane phase into reduced coenzyme Q10 by sodium hydrosulfite, a reducing agent (see Example 3 in Japanese Kokai Publication Sho-60-75294). Thus, the ratio of reduced coenzyme Q10 among the entire coenzymes Q10 in the microbial cells is not clear.
Furthermore, in both of the above (1) and (2), the production amount of coenzymes Q in culture are not described.
As described above, microbial cells containing reduced coenzyme Q10 at high ratio have not been reported yet. Still less, it has not been known a fermentation production of reduced coenzyme Q10 on the industrial scale, that is, a method comprising culturing microorganisms to obtain microbial cells containing reduced coenzyme Q10 at high ratio among the entire coenzymes Q10, and recovering reduced coenzyme Q10 to obtain high-purity reduced coenzyme Q10.
Under such circumstances, if a method for obtaining a large quantity of coenzyme Q10 containing reduced coenzyme Q10 at high ratio by culturing microorganisms is found, it can be a highly useful method for producing reduced coenzyme Q10 .